1. Field of the Invention
The present invention relates to a terminal used in a bulb socket for use in automotive lights and, more particularly, to a terminal positioned inside the bulb socket and having a contacting element whose deterioration of the spring characteristics is prevented to improve the contact reliability to the negative terminal of the bulb base.
2. Description of the Prior Art
In FIGS. 9 and 10, a conventional socket-side negative terminal 1 for use in a bulb socket 2 formed by bending a single thin metal band is shown. The socket-side negative terminal 1 comprises a bulb-side connecting element 1a for electrically connecting with the bulb 3 formed flexibly stamped out at one end portion thereof, and a connector 1b for electrically connecting with the external connectors provided at the other end portion thereof.
As shown in FIG. 11, the terminal 1 is inserted to an insertion channel 2c with a T-shaped cross section formed in a perimeter wall 2b of a bulb insertion opening 2a of the socket 2. The tip of the connecting element 1a protruding to the inside from the insertion channel 2c contacts the negative terminal face of the bulb base 3a inserted to the bulb insertion opening 2a.
The connector 1b of the terminal 1 protrudes into the connector insertion opening 2g from the insertion hole formed in the bottom wall 2f of the bulb insertion opening 2a, and contacts the external connector (not shown).
A positive terminal 4 formed by bending a single metal piece is inserted to a positive terminal insertion channel 2d, which is formed diagonally to the negative terminal insertion channel 2c of the socket 2. A bulb-side connector 4a contacts the positive terminal of the bulb bottom 3d, and the other connector 4d protruding from the bottom wall 2f connects with the external connector.
A bulb 3 depicted by an imaginary line is secured in the socket 2 by inserting from the top a pair of pins 3b, which protrude at the outside circumference of the bulb base 3a, into J-shaped pin insertion channels 2h formed in the bulb insertion opening perimeter wall 2b, and then turning the bulb 3 after insertion to secure the bulb 3 in the socket 2.
As best shown in FIG. 9, the bulb-side connecting element 1a of this conventional negative terminal 1 is stamped out at the center near the end of the thin metal band lc to project at a specified angle .theta.p and extends by a predetermined length Lc from the base 1d of the stamping and to flexibly contact the bulb base 3a with the contact 1e on the end of the projection.
When the negative terminal 1 shaped as described above is inserted to the socket 2 and contacts the bulb 3, the stamped base 1d of the connecting element 1a is positioned at the open end of the bulb insertion opening 2a approximately opposite the bulb base 3a, as best shown in FIG. 11.
When the bulb 3 is continuously turned on, the base 1d becomes hot because of the heat generated by the bulb 3. In particular, for example when a high output bulbs or double bulb are used for the bulb 3, the temperature at the base 1d sometimes reaches approximately 180.degree. C.
When the base 1d of connecting element 1a gets hot, the spring characteristics thereof deteriorate so that the contact pressure of the contact 1e drops, and the contact resistance at the circumference of the bulb base 3a increases. This causes the already high temperature to rise further, resulting eventually in non-conductivity.
The deterioration of the spring characteristics of the base 1d will be described with reference to FIGS. 12A, 12B, and 12C. Since the connecting element 1a initially has sufficient spring, the connecting element 1a extrudes from the terminal 1 by a predetermined length To and positioned thereat, an original position inside the bulb insertion opening, as indicated by the imaginary line in FIG. 12A. When the bulb 3 is inserted in the bulb socket 2, the connecting element 1a is pressed by the bulb base 3 so that the connecting element 1a is moved from the original position to a contacting position at which the connecting 1a is resiliently contacted with the bulb base 3, as indicated by a solid line.
However, as the spring characteristics of the base 1d deteriorates, the connecting element 1a will eventually not return to the original position and stops at a deteriorated position below the terminal 1 by a length Td, as indicated by a imaginary line in FIG. 12B, even when the bulb 3 is removed from the socket 2. In this case, when other bulb 3 with a smaller base diameter is inserted into the socket 2, a gap Tg occurs between the outside circumference of the bulb base 3a and the contact 1e, as shown in FIG. 12C. Thus, the connecting element 1a can not contact with the bulb base 3a, resulting in the lack of conductivity between the terminal 1 and the bulb 3.